Fix how block_states are constructed for transition to contain correct validation tree data

[arhag]

Transition creates block_states from transition blocks by computing the next block_state starting from the block_state of the IF Genesis block. The way this is currently done does not capture the Savanna action_mroots and so it constructs block_states that have a valid_t with incorrect data (specifically an empty digest for the action_mroot).

This code needs to be corrected to incorporate the correct action_mroots into the block_states constructed during the transition. We should disallow any constructor from being able to build a block_state with essential data missing.